58 
MR. GROVE ON THE EFFECT OF 
Upon the whole, we may conclude, from the experiments detailed in this paper, 
that the cooling effect of different gases, or rather the difference in the cooling effect 
of hydrogen and its compounds from that of other gases, is not due to differences 
of specific heat ; it is not due to differences of specific gravity ; it is not due to dif- 
ferences of conducting powers for electricity; it is not due to the character of hydrogen 
in relation to its transmission of sound, noticed by Leslie, for reasons which I have 
before given* ; it is not due to the same physical characters of mobility which occa- 
sion one gas to escape from a small aperture with greater facility than another ; but 
it may be, and probably is, affected by the mobile or vibratory character of the particles 
by which heat is more rapidly abstracted. I at one time thought that the effect might 
have relation to the combustible character of the gas, and that the electro-negative 
gases were in respect to it contra-distinguished from the electro-positive or neutral 
gases, but the experience I have obtained from the experiments detailed here induees 
me to abandon that supposition. 
1 incline to think, that, although influenced by the fluency of the gas, the pheno- 
menon is mainly due to a molecular action at the surfaces of the ignited body and of 
the gas. We know that in the recognised effects of radiant heat, the physical state 
of the surface of the radiating or absorbing body exercises a most important influence 
on the relative velocities of radiation or absorption ; thus, black and white surfaces 
are, as every one knows, strikingly contra-distinguished in this respect : why may 
not the surface of the gaseous medium contiguous to the radiating substance ex- 
ercise a reciprocal influence ? why may not the surface of hydrogen be as black, and 
that of nitrogen as white to the ignited wire ? This notion seems to me the more 
worthy of consideration as it may establish a link of continuity between the eooling 
effects of different gaseous media and the mysterious effects of surface in catalytic 
combinations and decompositions by solids such as platinum. Epipolic actions will, 
I feel convinced, gradually assume a much more important plaee in physics than 
they have hitherto done ; and the further development of them appears to me the 
most probable guide to the connection by definite conceptions of physical and che- 
mical actions. 
The difference of the eooling effect of hydrogen, and of those of its compounds, 
where it is not neutralized by a powerful electro-negative gas, from all other gases, 
is perhaps the most striking peculiarity of the phenomena I have described. The 
differences of effect of ail gases other than hydrogen and such compounds are quite 
insignificant when compared with the differences between the hydrogenous and the 
other gases. There are some phenomena which I have before observed, and which 
were, at the time I noticed them, inexplicable to me; but they now appear depend- 
ent on this physical peculiarity of hydrogen. Thus, if a jet of oxygen gas be kindled 
in an atmosphere of carburetted hydrogen, the flame is smaller than when the con- 
verse effect takes place. The voltaic arc between metallic terminals is also much 
* Fhiiosophicai Transactions, 1847. 
